Lamp exhaust method



943- E. F. LowRY ETAL 2,334,713

LAMP EXHAUST METHOD Filed Dec. 27, 1941 3 Sheets-Sheet l AEGON FLUSHzo'ueu VACUUM F'l NE VACUUM FINE VACUUM m EOUGH ROUGH VACUUM AQGON FILL.

EOUGH Q NITROGEN VACUUM I LEAK DETEcTo FLUSH Q [zoueu FACTORY VACUUMFig.1

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ATTOIZNE Y Nov. 23, 1943. E. F. LOWRY ETAL Filed Dec. 27, 1941 5Sheets-Sheet 2 Erwin F. Lowry AND Jam e s LCOX, INVENTORS Fig. 5

BY i? v ATToQA/EY No v. 23, 1943. E, F, LQWRY HA 2,334,718

LAMP EXHAUST METHOD Filed Dec. 2'7, 1941 3 Sheets-Sheet 3 Pre Furnac esTeps T I fi'fm'i'? fim I v 6 l rough evacxmhom P r Fuhn QCQ sreps t I o1 ron n evacuation 7 l mgi f 1 Furnace lrlfroduce merr 5 2| mm aevqcunflon 8 opporfum'fy for v H 9 Tes fo learwae introduce mgr wIntroduce inerf gas 23 run n evacuah'cm H g mjrodqce meri' gas Introducemart 18 26%) fme eyocuofion m Troduce inert 03 J9me evacumion 3|introduce, mart gas mrroduce l'nerr gas dnsmounf envehpe 2-3 from ownerroun evacuation l c on '6 fne eva nah bremtmercury bomb E b ts lmfroduceinerr 520s I J mesb. COX INVENTORS BY;: '3 A ORNEY Patent'ed Nov. 23,1943 I UNITED STATES PATENT orrlca zswm Danvers, Mala,

assignors to Srlvania Electric Products Inc., a corporation ofMassachusetts Application December 27, 1941, Serial No. 424,808

6 Claims. (Cl. 176-3) This invention relates to electric gaseousdischarge lamps and more particularly to fiuorescent lamps and themethod of evacuation and filling thereof before they are finally sealed.

An object of. this invention is to provide a process for treating thelamps on an exhaust machine.

.Another object is to include in this process the heating of the lamp, aseries of flushing and evacuating steps, the introduction of mercuryinto the lamp, the utilization of vaporized mercury in fiushing andevacuating, the introduction of a final filling of an inert gas, and thefinal sealing of the lamp.

A further object is to provide a process for treating the lamps whichwill eliminate some of the causes of yellow bands, dark ends, "snakersand other undesirable characteristics which may be found in some lamps.A snaker is a lamp cycle. These steps and processes are accomplished ona rotary turret type exhaust machine through a plurality of heads aboutthe periphery thereof. A separate pump is used for each manifold, orgroup of interconnected positions.

Figure 2 is a plan view of the fixed valve plate and the plurality ofmanifolds associated therewith.

Figure 3 is a detail of the movable valve plate.

Figure 4 is a block diagram of the process steps of this invention.

Stations 2, 3, 4 and 5 may be used for loading and unloading the lamps.At these stations, a

lamp to be treated is connected to one of the v heads, or a lamp whichhas passed through the cycle and has been finally sealed at station I iswithdrawn from the machine. At station 6 the lamp is connected to avacuum pump. This connection has a restriction and a trap therein toprevent an evacuation with such speed that some of the coating ofluminescent material on the walls of the lamp would be drawn off.

Stations 1 and 8 are plugged positions, the lamp at these two positionsbeing disconnected from the rest of the exhausting apparatus in order toput it in condition to re tested at station 9 to determine whether ornot it is leaking. By

providing one or more stations, after the first evacuation station, forair to seep into the lamp, the lamp may be connected at a subsequentstation, such as station 9, to some suitable leakdetecting mechanism,thereby determining at the start of the exhausting cycle whether or notthe lamp leaks. By providing suitable pinching-off mechanism to operatein conjunction with the leak-detecting mechanism, the head to which aleaky lamp is connected may be effectively disconnected from the systemfor the remainder of the cycle, thereby preventing the leaky lamp fromdeleteriously affecting any of the other lamps during the exhaust cycle.

An elongated curved oven is disposed to enclose the lamps from stationsI to l9 As the machine indexes from station! to ,station 8, the

'lamp enters the oven, andas the machine indexes from station ill tostation is, the lamp comes out of the oven. One of the purposes ofheating the lamp is to assist the evacuating and flushing apparatus inobtaining a high purity atmosphere in the lamp.

At stations II), II, l2 and I3, the lamp is alternately connected to asupply of inert gas, such as argon, or a gas inert with respect to thisparticular process, such as nitrogen, and flushed, and then connected toa vacuum pump such as that marked "rough vacuum" and shown-as connectedto stations H and I3 in the accompanying figure. In positions In and. I2the lamp flushing takes place at one of the positions rather thanbetween positions as is done subsequently to insure removal of as muchof the residual gases originally in the lamp aspossible before the finerevacuation takes place.

During the rest of its stay in the oven, the lamp is subject to a seriesof flushing and evacuating steps. The use of more than one pump in thisprocess enables the attainment of a higher degree of evacuation in thelamp. Thus between stations I4 and I5, I6 and I1, and i8 and IS, a

I quantity'of an inert gas such as argon is introduced into the lamp. Ithas been found that a suitable quantity of the inert gas may beintroduced as the rotatable turret indexes to carry the lamps from onestation to another. Thus there is made available a greater number ofstations for evacuation. As may be notedfrom the accompanying schematicdiagram the stations.

- immediately following the several flushing steps,

1. e., stations l5, l1 and I9 are connected to one pump whereas thestations further removed from the flushing points, 1. e., stations 14,i6, and iii are connected to a separate pump. This. ar-

rangement increases the efiiciency of the pumps and enables theattainment of a finer degree of vacuum, for the pump immediatelyfollowing the fiush will draw off the major portion of the residualgases mixed with the flushing gas, thereby insuring a better degree ofvacuum on the next pump and enabling a finer degree of purification andevacuation of the lamp at that position. If the same pump were used forboth rough and fine vacuum, then the gases in the lamp on the roughvacuum might back up and get into the lamp connected to the fine vacuum,thereby preventing the attainment of a finer degree of vacuum at thisposition.

Not only is the lamp heated, flushed and evacu ated at the severalstations in the oven, but the filamentary electrodes thereof areconnected to a source of electrical energy while the lamp is in the'oven.

The fundamental object in this heating or cathode break-down is toobtain a filamentary electrode or cathode with high emissive qualities.Since one or more of the alkaline earth oxides may be used for thispurpose, it has been found that barium and strontium oxide is desirable.

Since it is advantageous to use a barium and strontium carbonate oracetate or other decomposable compounds of the alkaline earth roup andlacquer solution or other suitable dispersing or suspending media, whencoating the coiled wire, usually of tungsten, which forms the surface onwhich the barium and strontium xide is desired, the barium and strontiumcarbonate or acetate and dispersing or suspending medium must be brokendown so a to leave an active barium-strontium oxide with high emissivequalities. This break-down is accomplished by a series of filamentheating steps in which a current flows through the filamentaryelectrodes. The heating of the filament will cause the reduction of thebarium and strontium carbonates or acetates to their respective oxides.'Carbon dioxide and de-- composition products of lacquer will be drawnoff in th gaseous state.

The heating of the electrodes may be started at station l5 and continuedon for several stations after the lamp leaves the oven. Care should betaken in heating the cathodes that they are not heated too quickly forif this is done, the tungsten wire may break, the walls of the lampbecome discolored, or the electron emissive material may break up andchip off. Thus the voltage must be kept below the point where any one ofthese conditions might take place.

We have found that facility in evacuation and the attainment of a highdegree of purity in the lamp may be furthered by the utilization ofmercury vapor in driving off. the carbon dioxide and decompositionproducts of the lacquer. This may be accomplished by introducing mercuryinto the lamp preferably in the manner described in copendingapplication Serial Number 400,216 filed June 28, 1941, issued May 19,1942, as Patent No. 2,283,189, although the mercury may well beintroduced in a diiferent manner, for example, by causing a quantitythereof to be dropped down through the exhausttubulation from a suitabledispensing device mounted in register with the exhaust tubulation. Asshown in the co-pending application, the mercury is enclosed in a metalcontainer or bomb and electrically connected to the filamentaryelectrode at that end of the lamp further removed from the tubulationthrough which the lamp is being evacuated.

The heat of the oven and the degree to which the filamentary electrodeadjacent the mercury bomb is heated are adjusted to control the point oftime at which the bomb breaks and releases the mercury. It has beenfound desirable to have the mercury released just before or just afterthe lamp leaves the oven because it i at this point in the exhaust cyclethat the lamp is, at its highest temperature. flushing agent, of thereleased mercury which vaporizes is obtained, for it is when the lamp ishottest that the sweeping of the carbon dioxide and the decompositionproducts of the lacquer from the lamp is most desirable. If one waitsuntil the lamp cools down before flushing with the mercury, some of theforeign gases are liable to be absorbed by the fluorescent powder on thewalls of the lamp.

The mercury bomb may be broken to release the mercury contained thereinby raising the current through the cathode to which it is connected,sufiiciently so that the voltage drop across the cathode is high enoughto ionize the gas around it and cause a discharge to pass between thecathode and the mercury bomb connected to an end thereof. The point oftime during the exhaust cycle at which the mercury is released is quiteimportant. If the mercury is released and permitted to vaporize while asubstantial portion of the carbon dioxide and decomposition products ofthe lacquer are still present in the lamp, there is a tendency for themercury and oxygen to combine and form mercuric oxide which in turn hasbeen one of the causes of discoloration, for example yellow bands aroundthe wall of the lamp adjacent the cathode.

A highly emcient use of the mercury released by the bomb as a flushinmeans may be flushes with the same mercury as one of the flushing agentsmay be obtained.

When the lamp comes out of the oven, an arrangement, similar to the oneemployed when the lamp was in the oven, is used, with respect toflushing and evacuating. Stations l9, 2|, 23 and 25, are locatedimmediately following the introduction of a quantity of argon and thesweeping back into the lamp of the condensed mercury for flushingpurposes. The major portion of the foreign gases will be drawn oil bythe vacuum pumps connected to these positions while separate pumps towhich stations 20, 22 and 24 are connected will enable the attainment ofa higher degree of vacuum before the next flush.

The cathode lighting steps mentioned above are continued after the lampleaves the oven and are continued until the lamp reaches station 30.Although the number of stations at which the cathodes are heated maywell vary, it has been found that a cathode with better emissivequalities may be obtained by gradually heating the cathode at severalstations rather than subjecting it to intensive heating at a fewstations. 1

Positions 26 to 30 inclusive are devoted to evacuating, the flushingbeing discontinued after station 25. The mercury which has been utilizedThus maximum eillciency, as a as a flushing agent will have condensedoutside the lamp during the evacuation at station 25. Such other mercuryas vaporizes while the lamp is being evacuated at stations 26 to 30inclusive will also condense with the previously vaporized mercury. Twoor more separate pumps are used during the evacuation at stations 26 to30 inclusive in order to obtain the highest degree of vacuum before theintroduction of a quantity of inert gas which is to be sealed in thelamp.

This filling of gas is introduced as station 3|.

The accurate measurement of the desired pressure of argon may beaccomplished in any one of several ways. However, I have found that theintroduction of argon in excess of the desired amount at station 3| andthen drawing oif the excess at station 32 is preferable for a higherdegree of accuracy is automatically assured. Apparatus such as thatshown in U. S. Patents 2,267,274 or 2,267,594 is suitable for thispurpose. This final filling of argon will sweep the condensed mercuryback into the lamp in which it will be finally sealed at station i.

One of the major advantages of the above-described exhaust cycle is thatit enables the evacuation of large lamps to a high degree of purity ofatmosphere in an exceedingly short time. For example, a lamp ofapproximately 75 cubic inches in volume may be passed through thisexhaust cycle in about 5 /2 minutes. This is made possible to a greatextent by the mercury vapor released from the bottom of the lamp to actas a difiusion pump. From the time the mercury is released at or aboutstation [9, there is a continuous vaporization thereof thus serving as adifiusion pump. Not only does the vaporized mercury act in conjunctionwith the argon at stations to where argon is periodically introduced andexacuated but it also is very efl'ective in sweeping residual gases fromthe lampat stations 26 to 30 where the sole operation on the lamp is oneof evacuation. It is important that this mercury be located andvaporized at the bottom of the lamp, i. e., at the end further removedfrom the end through which evacuation takes place, because otherwise itwill hinder rather than aid in the obtaining of a high degree of purityof atmosphere in the lamp due it actin as a ceiling over the residualgases.

In Figure 2, the multiplicity of manifolds are shown connected to thefixed portion of the valve through which the evacuation and gas-fillingof the lamp during the exhaust cycle takes place. The sweeps 33 connectthe flushing manifolds 34 and the rough and fine vacuum manifolds 35 tothe fixed valve plate 38. The plurality of ports 38 in the movable valveplate 39 shown in Figure 3 are successively placed in register with theplurality of ports 31 in the fixed valve plate 35 as the rotatableturret to which the movable valve plate 39 is connected carries thelamps connected thereto through the exhaust cycle. It is in this mannerthat a lamp which has been placed in register with one of the ports 38in the valve plate 38 is successively brought into register with the 5What we claim is:

1. A process for exhausting an electric discharge device havingelectrodes containing a quantity of elect'ron-emissive material, saidprocess comprising: heating said device in an oven; alternately flushingwith an inert gas and evacuating said device while in said oven;electrically heating said electrodes while said device is in said oven;removing said device from said oven; alternately in short stepsflushing, with a combinatlon of an inert gas and mercury vapor, andevacuating said device after it is removed from said oven; introducing afinal quantity of an inert gas into said device; and sealing saiddevice.

2. A process for exhausting an electric discharge device havingelectrodes containing a quantity of electron-emissive material, saidprocess comprising: heating said device; alternately flushing with aninert gas and evacuating said device; heating the electrodes of saiddevice; aiternately in short steps flushing, with a combination ofmercury vapor and an inert gas, and evacuating said device; introducinga final quantity of an inert gas into said device; and sealing saiddevice.

3. A process for exhausting an electric discharge lamp havingfilamentary electrodes, said process comprising the following steps:exhausting the lamp to a rough vacuum; baking the lamp in an oven;alternately flushing the lamp with an inert gas and evacuating the same,said alternation comprising introducing a quantity of inert gas intosaid lamp, evacuating said lamp to a rough vacuum on one pump, andevacuating said lamp to a fine vacuum on a second pump; heating thefilamentary electrodes of said lamp; alternately in short steps flushingsaid lamp, with a combination of an inert gas and vaporized mercury, andevacuating the same, said alternation being the same as said firstalternation; and sealing said lamp.

4. A process for exhausting electric discharge devices having electrodescontaining a quantity of electron-emissive material, said processcomprising: heating said device in an oven; alternately flushing with aninert gas and evacuating said 7 device while it is in said oven; heatingthe electrodes of said device while said device is in said oven;withdrawing said device from said oven; alternately in short stepsflushing with mercury vapor and evacuating said device after it iswithdrawn from said oven; introducing a final quantity of an inert gasinto said device; and sealing said device.

- 5. In a process for exhausting an electric discharge device, a seriesof short steps of alternately flushing said device with a combination ofan inert gas and mercury vapor and evacuating said device.

6. In a process for exhausting an electric discharge device, the stepsof vaporizing a quantity of mercury at the end thereof further removedfrom the end of evacuation, and alternately in short steps flushing saiddevice with a combination of an inert gas and mercury vapor andevacuating said device.

ERWIN F. LOWRY. JAMES L. COX.

